James R. Williams

RRGGBBAA! What sounds like some guttural scream of a developer trying to vertically center something in a page without Flexbox, is actually a nifty new CSS property that is working its way into the specification in the form of CSS Color Module Level 4.

As the name suggests, this is the next evolution of color notion in web development. Including things like LCH (Lightness Chroma Hue 1) colours and currentcolor. One of the more eye-catching sections of the spec for me is the new opacity notation for hex colors.

Where the common notations for hex colors are the shorthand three digits (#RGB) and six digits (#RRGGBB). The new additions are a new 8 and 4 digits color notations, adding one or two character space for the alpha (opacity) channel. No more translating to rgba if you want a slightly transparent color! Simply add another number to shorthand hex to opacity! Here is a quick sample of its usage:

span:nth-child(1) {
  /* Your regular RGB hex code. */ 
  background: #000;
}
span:nth-child(2) {
  /* A new hex code that is 90% opaque */ 
  background: #0009;
}
span:nth-child(3) {
  /* A new hex code that is 55% opaque */ 
  background: #00000055;
}

I also put together this CodePen demo for a more interactive demonstration: jamesrwilliams/pen/rNOjBLQ

Browser Support

While the spec is a CSSWG Editor' Draft (at the time of writing), support for it is somewhat impressive. Globally the new CSS Color Module L4 is supported by ~92.53% of users base on caniuse.com. No support on IE or Opera Mini and some others low usage browsers.


  1. Lea Verou wrote a great summary of LCH and how it is going to be a game changer for web development back in April you should read: "LCH colors in CSS: what, why, and how?".